1. Field of the Invention
The present invention relates to a printer and a method of switching ribbon tracks of an ink ribbon, and, more particularly, to a scheme of suppressing a decrease in ink density to prolong the service life of a single ink-ribbon cartridge and to prevent the occurrence of a significant variation in printing density on the same page.
2. Description of the Related Art
An ink-ribbon cartridge 101, as shown in FIGS. 12 and 13, is mounted on a printer of a wire-dot matrix type, for example. This type of ink-ribbon cartridge 101 comprises a case 103, and an endless type ink ribbon 105 retained in the case 103. This ink ribbon 105 consists of a single ribbon track so that the same ribbon track is repeatedly used.
The prior art structure has the following drawback. Since the ink ribbon 105 consists of a single ribbon track, the same ribbon track is used over and over again, causing the printing density to become low relatively earlier, as mentioned above. This inevitably shortens the life of the single ink-ribbon cartridge 101. This requires the frequent replacement of the ink-ribbon cartridge 101, which is troublesome.
The above problem will now be described more specifically with reference to FIG. 14. In FIG. 14, for example, a ribbon track area extending from a.sub.2 to b.sub.2 is used to print on a printing page P.sub.1, a ribbon track area extending from b.sub.2 to c.sub.2 is used to print on a printing page P.sub.2, a ribbon track area extending from c.sub.2 to d.sub.2 is used to print on a printing page P.sub.3, and a ribbon track area extending from d.sub.2 to e.sub.2 is used to print on a printing page P.sub.4. The endless type ink ribbon 105 loops back and the same ribbon track areas will be used again. In other words, the same ribbon track areas are always repeatedly used. Accordingly, the printing density quickly becomes lower, and the life of the ink-ribbon cartridge 101 expires quickly.
The prior art systems are disclosed in, for example, Japanese Examined Patent Publication Nos. sho 40-28861 and sho 51-11528.